1. Field of the Invention
The present invention is related to regeneration and reactivation of spent or deactivated catalysts used in hydrorefining processes, and, more particularly, to a method for regenerating deactivated catalysts employed in hydrodesulfurization.
2. Description of the Prior Art
Hydrorefining of hydrocarbons is usually carried out with a particulate catalyst comprised of a refractory oxide support containing Group VIB and Group VIII metals. Typically, catalysts comprising cobalt and molybdenum components supported on alumina are utilized in hydrodesulfurizing hydrocarbon feedstocks so as to reduce high concentrations of sulfur as well as contaminant metals such as vanadium and nickel. Although these catalysts are highly useful in reducing sulfur and contaminant metals from hydrocarbons, the activity of such catalysts is diminished during the course of processing as a result of deposition of contaminant metal and carbon residues (coke) on the catalyst. Coke deposit reduces the effective surface area and pore size of the catalyst, while the heavy contaminant metals, particularly vanadium, tend to poison the catalyst and plug the pores. During the course of processing, the operating temperature must be increased to compensate for the coking, plugging, and poisoning effects, but the higher temperature increases coking and further deactivates the catalyst. Eventually, the required temperature increase to maintain a desired amount of sulfur and metals removal becomes intolerable, and the catalyst is removed, deactivated due to metals and/or coke deposits.
Regeneration of coked and metal-contaminated catalysts back to a catalytically active form has been the subject of much investigation, and a number of approaches for regenerating hydrodesulfurization catalysts by removal of deposited metals have been developed. Acidic media such as mineral acids, anhydrous HF, oxalic acid, other carboxylic acids and even acidified amine solutions have been employed. Other approaches include the use of hydrogen peroxide and chlorinating agents, as well as high temperature treatment with sulfur, as note U.S. Pat. Nos. 3,562,150, 4,216,118, and 4,014,815, respectively. However, such approaches (1) do not restore a sufficiently high degree of catalytic activity, (2) result in loss of strength of the support material, or (3) result in an unacceptable loss of active metals, such that catalytic activity of the regenerated catalyst is considerably inferior to the fresh catalyst.
It is therefore an object of this invention to provide a method for regenerating a hydrorefining catalyst such that no appreciable loss of support strength and essentially full recovery of catalytic activity result.
Another object is to reactivate a deactivated hydrorefining catalyst by restoring an appreciable amount of active metal components to the catalyst as well as by removing essentially all the coke and maintaining or improving the support strength.
Still another object is to provide a hydrorefining process, and most particularly a hydrodesulfurization process, using catalysts reactivated by the method of the invention. These and other objects and advantages of the invention will become apparent from the following description.